The present invention relates to electronic testing systems, and more particularly to test probes for electronic testing systems.
The testing of samples is performed widely in the manufacture of products. For example, the manufacture and fabrication of integrated circuits begin with blank, unpatterned semiconductor wafers. These wafers undergo a number of critical testing steps before being processed and formed into the final integrated circuit form. For example, sheet resistance and wafer (substrate) thickness may be tested in the manufacturing process so that the bulk resistivity of a wafer can be determined.
Testing of sheet resistance, substrate thickness and other characteristics of a semiconductor wafer is often done using a probe assembly having a number of electrical contacts or pins capable of directing a constant current (I) through the film and reading the voltage drop (V) created across the film by the current. Sheet resistance may then be determined by Ohm""s law (R=K(V/I)), after which the thickness of the substrate may be calculated using the sheet resistance and the known bulk resistivity (xcfx81) of the film. The constant K is determined by the geometry of the probes in the specific configuration.
Because semiconductor wafers are manufactured from many types of materials, each of which exhibit specific characteristics, a different type of probe assembly may be required for a particular application. For example, probe assemblies with sharper pins (i.e. types xe2x80x9cAxe2x80x9d or xe2x80x9cBxe2x80x9d probes) are used for metal film. The sharp pin is utilized because it is able to push into the metal for good contact. On the other hand, probe assemblies with duller pins (i.e. types xe2x80x9cCxe2x80x9d or xe2x80x9cDxe2x80x9d probes) are used, for example, for doped silicon applications. Using a dull pin to contact silicon reduces the chance of puncturing the surface of the wafer. Other applications of semiconductor testing require probe assemblies that vary the spacing between the pins and electrical contacts or probe assemblies that apply a different force to the wafer surface (e.g. a spring-loaded pin).
In the prior art, probe assemblies were changed every time a different type of probe was required by a specific application (for example, changing from a type A to a type C probe). Probes were also changed for different applications because of the danger of contamination.
The conventional method of changing probe assemblies is to change it by hand. One problem with associated with this technique is that it increases the risk of error during the operation of the probe assembly. Removal of a probe assembly results in unnecessary wear and tear, which could lead to errors in measurement. Contamination and damage of the delicate probe is also a risk.
Yet another problem inherent in the replacement of a probe test head by hand is that the electrical connection between the probe assembly and the microprocessor controller of the electronic testing system must be broken, therefore increasing the risk for error if the probe assembly is not properly replaced. In addition, the procedure for manually changing probe test heads is impractical. For example, in an automated wafer handling system, each wafer is loaded onto the measurement equipment from a wafer cassette using robotics. Therefore, operators would need to halt the operation of the wafer testing system each time a probe test head needs to be changed.
Because it takes several minutes to manually changing probe test heads, if such a change is needed, it takes much longer to test each individual wafer, decreasing the overall efficiency of the wafer testing system. The changing of probe assemblies is so inconvenient and time consuming that multiple wafer testing systems are often used at considerable additional expense to solve the problem, with each wafer testing system having a different probe assembly.
It is also of importance, in any system where probes are changed, to provide accurate and repeatable mechanical positioning following probe changes. This can be especially important in systems that produce multi-point resistivity maps on semiconductor test wafers, since computed resistivity uniformity may be impacted by probe position reproducibility. Prior art systems, in many cases, have relied solely upon electronic sensors to establish sensor location via switch closures, but this method is susceptible to long term position drift and therefore reliability problems. It also requires lengthy and frequent calibration procedures. It is therefore desirable to have mechanical xe2x80x9chard stopxe2x80x9d positioning, with location verification via electronic sensors.
Despite the development of semiconductor technology and the importance of testing wafers accurately and efficiently, a convenient and reliable method and apparatus for changing test probe assemblies remain elusive. In view of the foregoing, what is needed is an efficient method and apparatus for changing probe assemblies for electronic testing systems.
The present invention fills this need by providing a method and apparatus for changing probe assemblies. Several inventive embodiments of the present invention are described below.
One embodiment of the present invention, a multiple test probe system is disclosed. The system includes a support, a probe bus comprising a plurality of wires and a mount rotationally coupled to the support and capable of rotating to a plurality of testing positions. A plurality of probe assemblies are coupled to the mount and associated with the plurality of testing positions, wherein each of the probe assemblies include a plurality of electrical contacts coupled to the plurality of wires of the probe bus regardless of a testing position of the mount. A Geneva Mechanism having a driven wheel provided with a plurality of slots, is attached to the mount for co-rotation therewith. A drive wheel is rotationally coupled to the support and provided with a drive member engaging one of the plurality of slots of the driven wheel. Rotation of the drive wheel relative to the support provides an incremental angular rotation to the driven wheel due to the engagement of the member with a slot, such that the position after a position when the member is disengaged from the slot coincides with at least one of the plurality of test positions. A motor coupled between the drive wheel and the support is disclosed.
In another embodiment of the present invention, a multiple test probe system is disclosed wherein the driven wheel comprises a plurality of radially extending slots and a concave cam follower guiding surface interposed between each pair of the radially extending slots. The drive wheel comprises a drive member and a restraining cam having a cylindrical convex surface, the drive member of the drive wheel being engaged with one of the radially extending slots to incrementally rotate the driven wheel through rotation of the drive wheel. The cylindrical convex surface of the drive wheel is engaged with the concave cam follower guiding surface of the driven wheel during a portion of time when the drive member is not engaged with the plurality of radially extending slots.
In another embodiment of the present invention, a multiple test probe system comprising a position sensor mounted at a contact position on the support, wherein the position sensor is activated to verify when at least one of the plurality of probe assemblies is in the testing position is disclosed.
In another embodiment of the present invention, a multiple test probe system wherein the position sensor is at least one of a microswitch, an optical sensor, and a magnetic sensor is disclosed.
In another embodiment of the present invention, a multiple test probe system wherein the electrical contacts are coupled to the probe bus in parallel is disclosed.
In another embodiment of the present invention, a multiple test probe system wherein each of the plurality of probe assemblies includes four electrical contacts is disclosed.
In another embodiment of the present invention, a multiple test probe system wherein the position sensor is placed to detect the drive member position during the portion of time the drive member is not engaged with the radially extending slots in the driven wheel is disclosed.
In another embodiment of the present invention, a multiple test probe system wherein at least one of the plurality of radially extending slots is shortened, such that engagement of the shortened slot with the drive member prevents complete rotation of the drive wheel is disclosed.
In another embodiment of the present invention, a method for providing a multiple test probe system is disclosed. The method provides a support, a probe bus comprising a plurality of wires, a mount rotationally coupled to the support and capable of rotating to a plurality of testing positions, and a plurality of probe assemblies coupled to the mount and associated with the plurality of testing positions. Each of the probe assemblies include a plurality of electrical contacts coupled to the plurality of wires of the probe bus regardless of the testing position of the mount. The method provides a Geneva Mechanism having a driven wheel having a plurality of slots, attached to the mount for co-rotation therewith, and a drive wheel rotationally coupled to the support and provided with a member engaging one of the plurality of slots of the driven wheel. Rotation of the drive wheel relative to the support provides an incremental angular rotation to the driven wheel due to the engagement of the member with a slot, such that the position after a position when the member is disengaged from the slot coincides with at least one of the plurality of test positions. The method also provides a motor coupled between the drive wheel and the support is disclosed.
In another embodiment of the present invention, a method for providing a multiple test probe system comprising a driven wheel having a plurality of radially extending slots and a concave cam follower guiding surface interposed between each pair of the radially extending slots is disclosed. The method provides a drive wheel having a drive member and a restraining cam having a cylindrical convex surface, the drive member of the drive wheel being engaged with one of the radially extending slots to incrementally rotate the driven wheel through rotation of the drive wheel and, engaging the cylindrical convex surface of the drive wheel with the concave cam follower guiding surface of the driven wheel during a portion of time when the drive member is not engaged with the plurality of radially extending slots.
In another embodiment of the present invention, a method for providing a multiple test probe system comprising providing a position sensor mounted at a contact position on the support, wherein the position sensor is activated to verify when at least one of the plurality of probe assemblies is in the testing position is disclosed.
In another embodiment of the present invention, a method for providing a multiple test probe system comprising providing the position sensor from at least one of a microswitch, an optical sensor, and a magnetic sensor is disclosed.
In another embodiment of the present invention, a method for providing a multiple test probe system comprising coupling the electrical contacts to the probe bus in parallel is disclosed.
In another embodiment of the present invention, a method for providing a multiple test probe system comprising providing four electrical contacts for each of the plurality of probe assemblies is disclosed.
In another embodiment of the present invention, a method for providing a multiple test probe system comprising placing the position sensor to detect the drive member position during the portion of time the drive member is not engaged with the radially extending slots in the driven wheel is disclosed.
In another embodiment of the present invention, a method for providing a multiple test probe system comprising shortening at least one of the plurality of radially extending slots, such that engagement of the shortened slot with the drive member prevents complete rotation of the drive wheel is disclosed.
One advantage of the present invention is that it allows a multiple probe system to efficiently change probe assemblies for different applications. The present invention eliminates the need to change probe assemblies by hand and further eliminates the need to dedicate more than one multiple probe system to different applications that require different types of probe assemblies. Another advantage of the present invention is that it reduces the chance of both wear and error because the electrical contacts of the probe assemblies are coupled to the probe bus regardless of the position of the mount.
The invention has been described herein in terms of several preferred embodiments. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention. Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the present invention. The embodiments and preferred features described above should be considered exemplary, with the invention being defined by the appended claims.